Process for preparing quinazolin-4-one derivatives

ABSTRACT

The present invention provides a novel process for preparing a series of quinazolin-4-one derivatives in high yields with reduced amounts of byproducts, the process comprising reacting, in the presence of a base, a trialkylsilyl halide with a compound represented by the formula ##STR1## wherein; R 5  is a phenyl group which may have 1 to 3 substituents each selected from a lower alkyl group, a lower alkoxy group or a halogen atom, a lower alkyl group, a phenyl-lower alkyl group which may have a halogen atom as a substituent on the phenyl ring, a lower alkenyl group, a lower alkoxy-lower alkyl group or a lower alkynyl group; R 6  is a lower alkyl group, a halogen-substituted lower alkyl group, a lower alkoxycarbonyl group or a phenyl group which may have, as a substituent, a lower alkyl group or a group of the formula ##STR2## wherein A is an oxygen atom or a single bond, Z is a lower alkylene group, R 7  is a lower alkyl group and R 8  is a lower alkoxy group, a phenyl group or a phenyl-lower alkoxy group which may have a halogen atom on the phenyl ring; 
     to produce the quinazolin-4-one derivatives which is valuable as pharmaceuticals or intermediates for synthesis thereof and represented by the formula ##STR3## wherein R 1 ,R 2 , R 3 , R 4 , R 5 , and R 6  are as defined above.

TECHNICAL FIELD

The present invention relates to novel processes for preparing quinazolin-4-one derivatives, in particular quinazolin-4-one derivatives which are valuable as intermediates for synthesis of compounds for use in pharmaceuticals for diabetes, or which are useful by themselves as active ingredients of therapeutic agents for diabetes.

BACKGROUND ART

Conventionally, quinazolin-4-one derivatives are prepared, for example by the process disclosed in J. Org. Chem., 41 (10), 1763 (1976) which comprises heating a diamide derivative for cyclization. However, since the process employs a high heating temperature (250° C. or above), it produces the quinazolin-4-one derivative in a very low yield and generates large amounts of byproducts.

An object of the present invention is to provide a novel process for preparing a series of quinazolin-4-one derivatives useful as pharmaceuticals or intermediates for synthesis thereof in higher yields with reduced amounts of byproducts.

The present inventors carried out extensive research and found that the following process can achieve the above object. The present invention has been accomplished based on the finding.

DISCLOSURE OF INVENTION

The present invention provides a process for preparing a quinazolin-4-one derivative, the process comprising reacting, in the presence of a base, a trialkylsilyl halide with a compound represented by the formula ##STR4## wherein R¹, R², R³ and R⁴ are the same or different and each represent a hydrogen atom, a lower alkyl group, a halogen atom, a nitro group, a lower alkoxy group, a cyano group, an N-lower alkylcarbamoyl group, a lower alkoxycarbonyl group or a halogen-substituted lower alkyl group, R⁵ is a phenyl group which may have 1 to 3 substituents each selected from a lower alkyl group, a lower alkoxy group or a halogen atom, a lower alkyl group, a phenyl-lower alkyl group which may have a halogen atom as a substituent on the phenyl ring, a lower alkenyl group, a lower alkoxy-lower alkyl group or a lower alkynyl group; R⁶ is a lower alkyl group, a halogen-substituted lower alkyl group, a lower alkoxycarbonyl group or a phenyl group which may have, as a substituent, a lower alkyl group or a group of the formula ##STR5## wherein A is an oxygen atom or a single bond, Z is a lower alkylene group, R⁷ is a lower alkyl group and R⁸ is a lower alkoxy group, a phenyl group or a phenyl-lower alkoxy group which may have a halogen atom on the phenyl ring;

to produce quinazolin-4-one derivative represented by the formula ##STR6## wherein R¹, R², R³, R⁴, R⁵ and R⁶ are as defined above.

More specifically, the present invention provides the processes as defined above wherein the base is a tertiary amine, wherein the trialkylsilyl halide is chlorotrialkylsilane, wherein the base and trialkylsilyl halide are used each in an amount of 3 to 20 equivalents, and wherein the reaction temperature is in the range of 0 to 100° C.

In the above formula representing the quinazolin-4-one derivative prepared by the process of the invention, the groups represented by R¹ to R⁶ are as follows.

The halogen atom may be a fluorine, chlorine, bromine or iodine atom.

Examples of the lower alkoxy group include methoxy, ethoxy, propoxy, isopropoxy, butoxy, tert-butoxy, pentyloxy, hexyloxy and like groups.

Examples of the lower alkyl group include methyl, ethyl, propyl, isopropyl, butyl, tert-butyl, pentyl, hexyl and like groups.

Examples of the phenyl-lower alkyl group which may have a halogen atom as a substituent on the phenyl ring include benzyl, α-phenetyl, β-phenetyl, 1-phenylpropyl, 2-phenylpropyl, 3-phenylpropyl, 4-phenylbutyl, 5-phenylpentyl, 6-phenylhexyl, 2-bromobenzyl, 3-bromobenzyl, 4-bromobenzyl, 4-chlorobenzyl, 4-fluorobenzyl, 4-iodobenzyl, 2-bromo-4-fluorobenzyl, 2-fluoro-4-bromobenzyl, 2-chloro-4-fluorobenzyl, 2-fluoro-4-chlorobenzyl, 2-bromo-4-chlorobenzyl, 2-chloro-4-bromobenzyl, 2-iodo-4-bromobenzyl, 3-chloro-5-bromobenzyl, 3-bromo-5-fluorobenzyl, 3-chloro-5-fluorobenzyl, 3-iodo-5-bromobenzyl, 3-chloro-5-iodobenzyl and like groups.

Examples of the lower alkenyl group include vinyl, 1-methylvinyl, 1-propenyl, 2-propenyl, 1-butenyl, 2-butenyl, 3-butenyl, 2,2-dimethylvinyl, 1-pentenyl, 2-pentenyl, 3-pentenyl, 4-pentenyl, 1-hexenyl, 2-hexenyl, 3-hexenyl, 4-hexenyl, 5-hexenyl and like groups.

Examples of the halogen-substituted lower alkyl group include trifluoromethyl, pentafluoroethyl, heptafluoropropyl, nonafluorobutyl, undecafluoropentyl, tridecafluorohexyl, chloromethyl, bromomethyl, iodomethyl, 2-chloroethyl, 3-chloropropyl, 4-chlorobutyl, 5-chloropentyl, 6-chlorohexyl and like groups.

Examples of the lower alkoxy-lower alkyl group include methoxymethyl, ethoxymethyl, propoxymethyl, butoxymethyl, pentyloxymethyl, hexyloxymethyl, 2-methoxyethyl, 3-methoxypropyl, 4-methoxybutyl, 5-methoxypentyl, 6-methoxyhexyl and like groups.

Examples of the lower alkynyl group include ethynyl, 2-propynyl, 3-butynyl, 4-pentynyl, 5-hexynyl and like groups.

Examples of the phenyl-lower alkoxy group which may have a halogen atom on the phenyl ring include benzyloxy, 2-phenylethoxy, 3-phenylpropoxy, 4-phenylbutoxy, 5-phenylpentyloxy, 6-phenylhexyloxy, 4-chlorobenzyloxy, 3-chlorobenzyloxy, 2-chlorobenzyloxy, 4-bromobenzyloxy and like groups.

Examples of the lower alkylene group include methylene, ethylene trimethylene, tetramethylene, pentamethylene, hexamethylene and like groups.

Examples of the N-alkylcarbamoyl group include N-methylcarbamoyl, N-ethylcarbamoyl, N-propylcarbamoyl, N-butylcarbamoyl, N-pentylcarbamoyl, N-hexylcarbamoyl and like groups.

Examples of the lower alkoxycarbonyl group include methoxycarbonyl, ethoxycarbonyl, propoxycarbonyl, butoxycarbonyl, pentyloxycarbonyl, hexyloxycarbonyl and like groups.

Examples of the lower alkanoyloxy group include acetoxy, propionyloxy, butyryloxy, valeryloxy, pivaloyloxy, hexanoyloxy, heptanoyloxy and like groups.

Examples of the phenyl group which may have 1 to 3 substituents each selected from a lower alkyl group, a lower alkoxy group or a halogen atom include phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-ethylphenyl, 4-propylphenyl, 4-butylphenyl, 4-pentylphenyl, 4-hexylphenyl, 2, 3-dimethylphenyl, 2,4-dimethylphenyl, 3,4-dimethylphenyl, 3,4,5-trimethylphenyl, 2-chlorophenyl, 3-chlorophenyl, 4-chlorophenyl, 4-bromophenyl, 4-iodophenyl, 4-fluorophenyl, 2,4-dichlorophenyl, 2,4,6-trichlorophenyl, 2-methoxyphenyl, 3-methoxyphenyl, 4-methoxyphenyl, 4-ethoxyphenyl, 4-propoxyphenyl, 4-butoxyphenyl, 4-pentyloxyphenyl, 4-hexyloxyphenyl, 2,3-dimethoxyphenyl, 2,4-dimethoxyphenyl, 3,4-dimethoxyphenyl, 3,4,5-trimethoxyphenyl, 4-chloro-2-methylphenyl, 2-chloro-4-methylphenyl, 4-methoxy-3-methylphenyl, 3-methoxy-4-methylphenyl, 4-chloro-2-methoxyphenyl, 2-chloro-4-methoxyphenyl, 3,5-di-t-butyl-4-methoxyphenyl and like groups.

Among the groups represented by R⁶ the phenyl group which may have, as a substituent, a lower alkyl group or a group of the above formula may be, for example, phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-ethylphenyl, 4-propylphenyl, 4-butylphenyl, 4-pentylphenyl, 4-hexylphenyl, 4- (diethoxyphosphoryl)methyl!phenyl, 3- (diethoxy-phosphorylmethyl!phenyl, 2- (diethoxy-phosphoryl)methyl!-phenyl, 4- (dimethoxyphosphoryl)-methyl!phenyl, 4- (dipropoxyphosphoryl)methyl!phenyl, 4- (diisopropoxy-phosphoryl)methyl!phenyl, 4- (dibutoxyphosphoryl)-methyl!phenyl, 4- (pentyloxyphosphoryl)methyl!phenyl, 4- (dihexyloxyphosphoryl)methyl!phenyl, 4- 2-(diethoxyphosphoryl)ethyl!phenyl, 4- 3-diethoxy-phosphoryl)propyl!phenyl, 4- 4- (diethoxyphosphoryl)-butyl!phenyl, 4- 5-(diethoxyphosphoryl)pentyl!phenyl, 4- 6-(diethoxyphosphoryl)hexyl!phenyl, 4- (ethoxyphenyl-phosphoryl)methyl!phenyl, 4- (methoxyphenylphosphoryl)-methyl!phenyl, 4- (phenylpropoxyphosphoryl)methyl!phenyl, 4- (butoxyphenylphosphoryl)methyl!phenyl, 4- (pentyloxy-phenylphosphoryl)methyl!phenyl, 4- (hexyloxyphenyl-phosphoryl methyl!phenyl, 4- (benzyloxyethoxyphosphoryl)-methyl!phenyl, 4- (4-chlorobenzyloxy)ethoxyphosphoryl!-methyl!phenyl, 4- (3-chlorobenzyloxy)ethoxyphosphoryl!-methyl!phenyl, 4- (2-chlorobenzyloxy)ethoxyphosphoryl!-methyl!phenyl, 4- (diethoxyphosphoryl)methoxy!phenyl, 3- (diethoxyphosphoryl)methoxy!phenyl, 2- (diethoxy-phosphoryl)methoxy!phenyl, 4- 2-(diethoxyphosphoryl)-ethoxy!phenyl, 4- 3-(diethoxyphosphoryl)propoxy!phenyl, 4- 4-(diethoxyphosphoryl)butoxy!phenyl, 4- 5-(diethoxy-phosphoryl)pentyloxy!phenyl, 4- 6-(diethoxyphosphoryl)-hexyloxy!phenyl or like groups.

According to the process of the invention, the compound of the formula (1) (starting material) is cyclized by reacting a trialkylsilyl halide with the compound in an inert solvent in the presence of a base.

Usable inert solvents are, for example, aromatic or aliphatic hydrocarbons such as benzene, toluene, xylene and petroleum ether, ethers such as diethyl ether, hydrocarbon halides such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane, etc.

Preferably usable bases are, for example, tertiary amines such as triethylamine, N,N-diethylaniline N-methylmorphorine, pyridine and 4-dimethylaminopyridine.

Preferred examples of the trialkylsilyl halide include chlorotrialkylsilanes such as chlorotrimethylsilane, chlorotriethylsilane, chloroethyldimethylsilane, chlorodimethylpropylsilane, chlorobutyldimethylsilane, chlorotripropylsilane, tributylchlorosilane and chloroethylmethylpropylsilane.

The amounts of the trialkylsilyl halide and base are not restricted but it is generally suitable to use them each in an amount of 1 to excess equivalents, preferably 3 to 20 equivalents. The reaction is carried out usually at temperatures ranging from 0 to 100° C. and is completed in a period of about 0.5 to 20 hours.

The starting material for use in the invention can be obtained, for example, by the process illustrated by the following reaction scheme. ##STR7## wherein R¹, R², R³, R⁴, R⁵ and R⁶ are as defined above, and Y is a halogen atom.

In the above reaction, the compound (A) is reacted with the acyl halide (B) in an inert solvent in the presence of a deacidifying agent. Usable inert solvents are, for example, aromatic or aliphatic hydrocarbons such as benzene, toluene, xylene and petroleum ether, ethers such as diethyl ether, ketones such as acetone, methyl ethyl ketone and acetophenone, hydrocarbon halides such as dichloromethane, chloroform, carbon tetrachloride and 1,2-dichloroethane, etc. Preferred examples of the deacidifying agent are amines such as triethylamine, N,N-diethylaniline, N-methylmorphorine, pyridine and 4-dimethylaminopyridine.

The acyl halide (B) is used preferably in an equimolar to small excess amount relative to the compound (A), and the deacidifying agent is used in an equimolar to excess amount relative to the compound (A). The reaction can be carried out generally at temperatures ranging from 0° C. to room temperature and is completed in a period of about 0.5 to 50 hours.

According to the invention, the contemplated quinazolin-4-one derivatives can be easily prepared in high yields. The obtained quinazolin-4-one derivatives are valuable as intermediates for synthesis of compounds for use in pharmaceuticals for diabetes, and useful by themselves as active ingredients of therapeutic agents for diabetes.

BEST MODE FOR CARRYING OUT THE INVENTION

The following Reference Example and Examples illustrate the present invention in further detail In the Reference Example, the compound for use as the starting material in the process of the invention was prepared.

REFERENCE EXAMPLE 1

27.2 g of 4- (diethoxyphosphoryl)methyl!benzoic acid was suspended in a mixture of 60 ml of dichloromethane and 2 ml of DMF. 13.1 g of thionyl chloride was added, and the resulting mixture was refluxed for 1 hour. After completion of reaction, the reaction mixture was allowed to cool and then slowly added dropwise, with ice-cooling and stirring, to a solution of 18.5 g of 2-(N-methylcarbamoyl)-5-chloroaniline in a mixture of 50 ml of pyridine and 30 ml of dichloromethane. After completion of addition, the resulting mixture was stirred at room temperature for 48 hours. Then, 50 ml of water was added to the reaction mixture to precipitate crystals. The crystals were then collected by filtration, fully washed with water and dried, giving 23.6 g of diethyl 4-{ 5-chloro-2-(N-methylcarbamoyl)phenyl!carbamoyl}benzylphosphonate.

Example 1

80 g (182.3 mmol) of the compound obtained in Reference Example 1 was dissolved in a mixture of 221 g (2184.0 mmol) of triethylamine and 2000 ml of dichloromethane. 87 g (800.8 mmol) of chlorotrimethyl-silane was slowly added dropwise to the solution with stirring at room temperature. After completion of addition, the resulting mixture was stirred with heating at 40° C. for 17 hours. After completion of reaction, the reaction mixture was concentrated and mixed with 1000 ml of 1N hydrochloric acid. The resulting mixture was subjected to extraction with dichloromethane. The organic layer was dried over magnesium sulfate, and the solvent was distilled off under reduced pressure. Diisopropyl ether was added to the residue for crystallization, and the crystals were collected by filtration. The obtained crude crystals were recrystallized from ethanol and water, giving 88.6 g of the contemplated diethyl 4-(7-chloro-3-methyl-4(3H)-quinazolinon-2-yl)benzylphosphonate.

Examples 2 to 13

The compounds shown in Tables 1 and 2 were prepared by following the procedures of Reference Example 1 and Example 1. The tables show the structures, melting points and yields of the compounds.

In the tables, Me, Et and Ph indicate methyl, ethyl and phenyl groups, respectively.

                                      TABLE 1     __________________________________________________________________________     1 #STR8##     Ex.       R.sup.1         R.sup.2           R.sup.3 R.sup.4                     R.sup.5  R.sup.6' Melting point (° C.)                                                Yield (%)     __________________________________________________________________________     1 H H Cl      H Me                              2 #STR9##                                         142˜142.5                                                93     2 H Br           H       H Et                              2 #STR10##                                       73˜74                                                66     3 H I H       H Me                              2 #STR11##                                       143˜144                                                81     4 H H           3 #STR12##                   H Me                              2 #STR13##                                       238˜239                                                83     5 H H           4 #STR14##                   H Me                              2 #STR15##                                       116˜117                                                85     6 H H H       H Me       H        135˜136                                                63     7 H H H       H Ph       H        157˜158                                                78     8 H H H       H --CH.sub.2 --CH═CH.sub.2                              H        81.5˜82.5                                                65     9 H H Cl      H Me       Me       125˜126                                                68     10       H H Cl      H Me                              5 #STR16##                                       192˜193                                                69     __________________________________________________________________________

                  TABLE 2     ______________________________________     6 #STR17##     Ex. R.sup.1               R.sup.2                     R.sup.3                         R.sup.4                             R.sup.5                                 R.sup.6                                        Melting point (° C.)                                                   Yield (%)     ______________________________________     11  H     Br    H   H   Ph  CF.sub.3                                        146˜147                                                   73     12  H     Cl    H   H   Ph  Me       183˜184.5                                                   72     13  H     H     Cl  H   Me  --COOEt                                        102.5˜103.5                                                   71     ______________________________________

Examples 14 to 49

The compounds shown in Tables 3 and 4 can be prepared in high yields by following the procedures of Reference Examples 1 and Example 1.

In the tables, Me, Et and Ph are as defined above, and iPr and Ac indicate isopropyl and acetyl groups, respectively

                                      TABLE 3     __________________________________________________________________________     7 #STR18##                                                     Bonding     Ex.       R.sup.1         R.sup.2           R.sup.3               R.sup.4                  R.sup.5      R.sup.7                                 R.sup.8      A   Z  position                                                          Melting point                                                          (° C.)     __________________________________________________________________________     14       H Br           Cl  H  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    144˜145                                              bond     15       H Br           NO.sub.2               H  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    177˜178                                              bond     16       H H CN  H  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    121˜122                                              bond     17       H H Cl  H  Me           Me                                 OMe          Single                                                  CH.sub.2                                                     4    109˜110                                              bond     18       H H Cl  H  Me           iPr                                 OiPr         Single                                                  CH.sub.2                                                     4    117˜118                                              bond     19       H Me           H   H  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    66.5˜67.5                                              bond     20       H Cl           Cl  H  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    Oil                                              bond        NMR(1)     21       H Cl           Cl  H  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    Oil                                              bond        NMR(1)     22       H Cl           Cl  H  Me           Et                                 OEt          O   C.sub.2 H.sub.4                                                     4    Oil                                                          NMR(2)     23       H H Cl  H  Me           Et                                 8 #STR19##   Single bond                                                  CH.sub.2                                                     4    143˜144     24       H H Cl  H  Me           Et                                 --OCH.sub.2 Ph                                              Single                                                  CH.sub.2                                                     4    Oil                                              bond        NMR(3)     25       F H H   H  --CH.sub.2 Ph                               Et                                 OEt          Single                                                  CH.sub.2                                                     4    96˜97                                              bond     26       H OMe           H   OMe                  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    99˜100.5                                              bond     27       H H --CF.sub.3               H  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    51˜52                                              bond     28       H H H   H  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    156˜156.5                                              bond     29       H OMe           OMe H                  9 #STR20##   Et                                 OEt          Single bond                                                  CH.sub.2                                                     4    103˜104     30       H H Cl  H  --OCH.sub.2 OMe                               Et                                 OEt          Single                                                  CH.sub.2                                                     4    123˜124                                              bond     31       H H Cl  H                  0 #STR21##   Et                                 OEt          Single bond                                                  CH.sub.2                                                     4    143˜146     32       H H Cl  H  Me           Me                                 OMe          Single                                                  CH.sub.2                                                     4    109˜110                                              bond     33       H H NO.sub.2               H  Me           Et                                 OEt          Single                                                  CH.sub.2                                                     4    125.5˜126.5                                              bond     __________________________________________________________________________                    Ex.             .sup.1 H--NMR (δ: ppm)  CDCl.sub.3     __________________________________________________________________________                                    !                    21              1.18 (6H, dt, J=4, 7)                                    3.08 (1H, dd, J=22, 15)                                    3.44 (3H, s), 3.67 (1H, dd, J=22, 15)                                    3.90-4.02 (4H, m), 7.32-7.59 (5H, m)                                    7.69 (1H, d, J=2), 8.28 (1H, d, J=9)                    22              1.37 (6H, t, J=7)                                    2.35 (2H, dt, J=19, 7)                                    3.52 (3H, s), 4.11-4.20 (4H, m)                                    4.27-4.37 (2H, m), 7.04 (2H, d, J=9)                                    7.43 (1H, dd, J=8, 2), 7.53 (2H, d, J=9)                                    7.71 (1H, d, J=2), 8.24 (1H, d, J=8)                    23              1.25 (3H, t, J=7), 3.23 (2H, d, J=22)                                    3.47 (3H, s), 3.94-4.15 (2H, m)                                    5.04 (2H, d, J=9), 7.35-7.52 (10H, m)                                    7.71 (1H, d, J=2), 8.23 (1H, d,     __________________________________________________________________________                                    J=9)

                                      TABLE 4     __________________________________________________________________________     1 #STR22##     Ex.       R.sup.1         R.sup.2             R.sup.3               R.sup.4                  R.sup.5   R.sup.6                                   Melting point (° C.)     __________________________________________________________________________     34       H Br  H H  Ph        --COOEt                                   164.5˜165.5     35       H Br  H H                  2 #STR23##                            Me     217˜218.5     36       H I   H H  Ph        Me     156˜157     37       H NO.sub.2             H H  Ph        Me     200.5˜222.5     38       H Br  H H                  3 #STR24##                            Me     155˜156.5     39       H H   H H                  4 #STR25##                            Me     116.5˜117.5     40       H Cl  H Cl Ph        Me     191.5˜192.5     41       H H   Cl               Cl Ph        Me     238˜239.5     42       H Cl  Cl               Cl Ph        Me     216.5˜217.5     43       Cl         Cl  Cl               H  Ph        Me     191.5˜193     44       H H   H H  Ph        Me     250 or above     45       H AcO H H  Ph        Me     191.5˜192.5     46       H H   Cl               H  Ph        Me     173˜174     47       H Br  H H  Ph        Me     180.5˜182     48       H H   Cl               H  Me        --CH.sub.2 --Cl                                   163˜164.5     49       H H   Cl               H  Me        CF.sub.3                                   120˜122     __________________________________________________________________________ 

We claim:
 1. A process for preparing a quinazolin- 4-one derivative, the process comprising reacting, in the presence of a base, a trialkylsilyl halide with a compound represented by the formula ##STR26## wherein R¹, R², R³ and R⁴ are the same or different and each represent a hydrogen atom, a lower alkyl group, a halogen atom, a nitro group, a lower alkoxy group, a cyano group, an N-lower alkylcarbamoyl group, a lower alkoxycarbonyl group, a lower alkanoyloxy group or a halogen-substituted lower alkyl group; R⁵ is a phenyl group which may have 1 to 3 substituents each selected from a lower alkyl group, a lower alkoxy group or a halogen atom, a lower alkyl group, a phenyl-lower alkyl group which may have a halogen atom as a substituent on the phenyl ring, a lower alkenyl group, a lower alkoxy-lower alkyl group or a lower alkynyl group; R⁶ is a lower alkyl group, a halogen-substituted lower alkyl group, a lower alkoxycarbonyl group or a phenyl group which may have, as a substituent, a lower alkyl group or a group of the formula ##STR27## wherein A is an oxygen atom or a single bond, Z is a lower alkylene group, R⁷ is a lower alkyl group and R⁸ is a lower alkoxy group, a phenyl group or a phenyl-lower alkoxy group which may have a halogen atom on the phenyl ring;to produce the quinazolin-4-one derivative being represented by the formula ##STR28## wherein R¹, R², R³, R⁴, R⁵ and R⁶ are as defined above.
 2. A process according to claim 1 wherein the base is a tertiary amine.
 3. A process according to claim 1 or 2 wherein the trialkylsilyl halide is a chlorotrialkylsilane.
 4. A process according to claim 1 or 2 wherein the base and trialkylsilyl halide are used each in an amount of 3 to 20 equivalents.
 5. A process according to claim 1 or 2 wherein the reaction temperature is in the range of 0 to 100° C.
 6. A process according to claim 3 wherein the base and trialkylsilyl halide are used each in an amount of 3 to 20 equivalents.
 7. A process according to claim 3, wherein the reaction temperature is in the range of 0 to 100° C.
 8. A process according to claim 4, wherein the reaction temperature is in the range of 0 to 100° C. 